Preparation of an Anti-Aggregation Silica/Zinc/Graphene Oxide Nanocomposite with Enhanced Adsorption Capacity

Nanomaterials play a significant role in adsorption treatment of dye wastewater, but irreversible aggregation of nanoparticles poses a significant problem. In this work, nanomesoporous zinc-doped silicate (NMSZ) was prepared by an in situ method. To prevent agglomeration, NMSZ was covalently bonded to graphene oxide (GO) sheets to form a nano-silica/zinc/graphene oxide composite (GO-NMSZ), aimed at removal of cationic dye methylene blue (MB). For comparison, undoped mesoporous silica (MS) was also synthesized and modified to obtain a silica/graphene oxide composite (GO-MS). The materials were characterized by powder XRD, SEM, FTIR spectroscopy, TEM, nitrogen sorption, and X-ray photoelectron spectroscopy (XPS). Preservation of the oxygen-containing groups of GO in the composites led to higher adsorption capacities. The best GO-NMSZ composite exhibited an enhanced adsorption capacity of 100.4 mg g^-1 for MB compared to those of undoped GO-MS (80.1 mg g^-1 ) and nongrafted NMSZ (55.7 mg g^-1 ). The nonselective character of GO-NMSZ is demonstrated by effective adsorption of anionic dye Congo red (127.4 mg g^-1 ) and neutral dye isatin (289.0 mg g^-1 ). The adsorption kinetics, adsorption isotherms, and a thermodynamic study suggested that MB adsorption occurs by chemisorption and is endothermic in nature.